The speed of data communications networks has been increasing steadily and substantially over the past several decades, requiring newly designed components to enable the networks to operate at these new higher speeds. As the speed of networks increases, the frequency at which electrical signals are transmitted over communications channels in these networks likewise increases. As a result, electrically conductive paths within the communications channels of the network, which presented no problems at lower frequencies, can become antennae that broadcast and receive electromagnetic radiation and cause errors in the data being communicated. This unwanted coupling of signals from one electrically conductive path to another is known as “crosstalk” and degrades the overall performance of the network. Unwanted crosstalk can occur between any proximate electrically conductive paths that physically form parts of the network, such as individual pairs of physical wires within a given communications cable, between or among nearby communications cables, and within connectors used to connect communications cables to desired electronic components, such as routers and network switches, within the network.
FIG. 1 is a diagram illustrating a portion of a conventional communications network 100 including a typical communications channel 101. The channel 101 includes a communications outlet 102 into which a communications plug 104 of a cable 106 is inserted to thereby connect a first electronic subsystem 108, such as a computer system, to the communications network 100. The communications outlet 102 fits within an opening 110 of a wall plate 112 to expose an aperture 114 in the communications outlet into which the plug 104 is inserted. Electrical signals are then communicated to and from the computer system 108 through the cable 106, plug 104, outlet 102 and a cable 116. The cable 116 includes another communications outlet 118 on the other end of the cable, with the communications outlet 118 often being part of another network component such as a patch panel 120. A second electronic subsystem 122, such as a network switch or other network component, is connected to outlet 118 through a cable 124 and plug 126 to interconnect the communications channel 101 to other components in the network 100 as indicated by the arrow 127.
The cables 106 and 116, plug 104 and 126, and outlets 102 and 118 are standardized components that include specified numbers of electrically conductive paths and a fixed configuration or arrangement of such paths within the plugs and outlets. Where the system 100 utilizes the Ethernet communications standard, for example, data is communicated through one or more twisted-pairs of conductive wires in the cables 106, 116. The plugs 104, 126 and outlets 102, 118 likewise include four corresponding pairs of electrically conductive elements or paths, such as in RJ45 outlets and plugs. For historical reasons, the physical arrangement of such electrically conductive paths within the plugs 104 and 126 is such that unwanted crosstalk is generated between pairs of electrically conductive paths. The outlets 102, 118, are designed in such a manner as to nullify the crosstalk generated by the plugs. As the speed at which data is communicated increases, so does the frequency range of operation for all components of the communications channel 101, making nullification of the unwanted crosstalk more difficult to achieve for reasons understood by those skilled in the art. This arrangement of electrically conductive paths within the plugs 104, 126 and outlets 102, 118 has nonetheless been retained even for current high-speed networks to provide compatibility between old and new network components.
As the speed or frequency at which networks operate continues to increase, crosstalk can become significant and can interfere with the proper operation of the network 100. There are generally two types of crosstalk. The first type of crosstalk occurs among the pairs of electrically conductive paths within an individual communications channel 101 and is termed “internal crosstalk.” Internal crosstalk is the unwanted signals communicated from one pair to another within a single communications channel.
The second type of crosstalk is known as “alien crosstalk” and occurs between or among pairs of electrically conductive paths in different communications channels 101. Alien crosstalk can be defined as unwanted signals communicated between pairs in different channels. Alien crosstalk can occur between most components of communications networks 100, and is particularly significant between those components which are physically located proximate to each other. For example, assume that nearby the cables 106, 116, plugs 104, 126, and outlets 102, 118 of the communications channel 101 of FIG. 1, there are several additional similar communications channels (not shown) having corresponding components. This would typically be the case in the network 100. In this situation, alien crosstalk can occur between the communications channel 101 and the additional physically proximate communications channels.
One particular type of alien crosstalk is known as “modal alien crosstalk” and is initiated by the unequal electrical exposures of some of the electrically conductive paths within the plugs 104, 126 to other comparable electrically conductive paths. These unequal electrical exposures result in a modal conversion of signals that causes unwanted electromagnetic waves of a different mode to propagate on electrically conductive paths in a given communications channel 101. These unwanted electromagnetic waves of a different mode can cause crosstalk in adjacent communications channels 101 that can interfere with the proper operation of such channels, particularly at the ever increasing frequencies at which networks operate. Since the outlets 102, 118 have conductors similarly arranged to those of the plug 104, 126 to be mechanically compatible, both the outlets and the plugs in a given channel cause modal conversion of signals. In addition, compensation circuitry used in the outlet to neutralize internal crosstalk can further add to the modal conversion of signals. Thus, both plugs and outlets contribute to the generation of modal alien crosstalk.
There is a need for improved communications outlets designed to neutralize the modal conversion of signals initiated in the plug, reduce that generated in the outlet itself, and reduce internal crosstalk without significantly increasing the complexity of manufacturing the outlet or its cost.